The present invention relates to forming three-dimensionally contoured articles such as automobile headliners. In the past, many automobile headliners have been formed by molding them of fiberglass reinforced polyester resin, often in a lay up molding process, as distinguished from thermoforming. One company molds such a product of glass reinforced polyester resin, laminated to a rigid urethane foam and covered by a soft urethane backed fabric. Such fiberglass reinforced polyester resin headliners act as a sound board, thus making the interior of the vehicle more noisy. Further, the lay up molding process is costly.
Some have eliminated the boardiness of fiberglass resin headliners by thermoforming a laminate comprised of a stiff structural yet thermoformable polystyrene foam layer and layers of kraft paper or a polymer film material bonded to either side of the foam. This laminate is covered with a soft polyurethane backed fabric. Thermoforming as opposed to lay up molding is cost effective. A laminate of a stiff polystyrene element with kraft paper or polymer film bonded to either side can be readily mass produced on automated equipment, cut into sheets, heated in a thermoforming operation and vacuum formed to shape. However, such headliners do not have sufficiently desirable sound absorbing properties because the kraft paper tends to reflect the sound rather than absorb it. The closed cell foam core itself is thought to be very effective in stopping sound transmission.
Many have endeavored to eliminate the paper or polymer film covering, from such laminates and substitute a nonwoven fabric mat on one or both sides of the stiff polystyrene foam element in order to achieve better sound absorbing properties. One problem with this and other thermoformable foam core laminates is that automobile headliners must be able to withstand relatively high environmental use temperatures, i.e., 185.degree. F. The structural foam polystyrene-fabric laminate tends to delaminate and/or sag when exposed to such high temperatures. One reason for this is that the adhesive used to adhere the laminate components together has to be thermoplastic or equivalent in order to be thermoformable. Thermoplastic adhesives of higher melting points tend to lack the desired adhesive ability for adhering the foam core layer to the outer layers of the laminate.
Those skilled in this art have spent years searching unsuccessfully for solutions to these problems As a result, thermoformed kraft paper or polymer film and structural foam polystyrene laminate and molded fiberglass reinforced polyester resin based laminates remain the principal automobile headliner constructions in use today.